Adenosine and analogues modified in the ribose moiety inhibit TSH, Gpp (NH)p and F-stimulated adenylate cyclase in beef thyroid membranes. The effect is markedly enhanced in the presence of Mn plus and is unaffected by theophylline. Since purine-modified analogues are inactive this response is characteristic of "p" site effectors in other tissues. We have also shown that lactoperoxidase binds to microtubules, oligomers and pure dimeric tubulin wth stoichiometries ranging from 0.3 to 2.0. The affinity constant for tubulin is 1.10 to the sixth power M and the reaction seems to be specific with respect to related proteins. The binding is being explored as a purification method and for histochemical purposes.